The present invention relates generally to data transfer systems, and more particularly to a method for sending data in a broadcast network.
Connection-oriented networks are traditionally associated with telephony and other types of communications where an association between a sender and receiver exists for a relatively long period of time (i.e. on the order of minutes). Connection-oriented communications is used when resources need to be nailed down to guarantee that the data is received and processed by the proper destination terminal. Connection-oriented communications is typically used for data which is sensitive to delay and/or delay variation.
The process of exchanging information on a connection-oriented network usually requires some signaling between the source and destination (and possibly a network manager) to negotiate the parameters of the connection before any useful data is exchanged. This is efficient when the delay required for signaling is small relative to the duration of the time spent to exchange information. The Asynchronous Transfer Mode (ATM) protocol is typically used for data message transfers in connection-oriented communications because it is a relatively fast, highly reliable switching protocol.
In contrast, connectionless networks such as the global Internet, are traditionally associated with computer networks and other types of communications where an association between a sender and receiver exists on a per-packet basis (i.e. on the order of milliseconds). Connectionless communication networks do not utilize advance signaling before sending data; therefore, there is no opportunity for the network to evaluate whether a given transmission can be guaranteed to reach its destination in a timely manner. Connectionless communications is typically used for lower priority data, such as Internet Protocol (IP) data, where it is not imperative that data will arrive at and be processed by the proper destination terminal. The connectionless protocol used by the global Internet, is referred to as a xe2x80x9cbest effortxe2x80x9d protocol.
Once a geosynchronous satellite is introduced into the path between the source and destination or between the source and the network manager, the cost in delay of performing connection-oriented communications is exacerbated. For connection-oriented communications over a satellite with an on-board cell relay switch, to establish a communications link between a source terminal and a destination terminal, the following steps need to be conducted:
a) A request is sent from the source terminal over the satellite to the Network Operations Center (NOC) asking for a connection identification address (CID) for the destination terminal and a channel for communications.
b) A channel and CID and path through the satellite cell switch are allocated by the NOC.
c) The channel allocation, CID, and path through the satellite cell switch are sent to the satellite.
d) The channel allocation and CID are sent to both the source terminal and the destination terminal.
Although this set-up procedure requires a significant amount of time, it accomplishes many purposes the most significant of which is that a path from a satellite uplink to a satellite downlink is created through the satellite network for the routing of cells with the header CID. In addition, the source terminal will know that it can use the allocated channel for communication with the desired destination terminal; the desired destination terminal will listen only to the allocated channel and accept only the packets with the proper CID in the header; and, other destination terminals do not use their resources to accept packets not intended for their use freeing up resources for communications with other source terminals.
After the set-up procedure is completed, to send a message from the source terminal to the destination terminal, the following additional steps must be completed:
a) The source terminal divides the message into cells in accordance with a predetermined adaptation layer protocol, if the message is longer than a single ATM cell. As required by the adaptation layer protocol, each cell includes a header. The source terminal places the allocated CID into the proper location in the header of each cell.
b) The cells are sent to a satellite.
c) Each cell is routed to the downlink antenna which covers the desired destination terminal.
d) The cells are broadcast by the downlink antenna.
e) The cells with the proper CID in the header are accepted by the destination terminal and reassembled back into the original massage.
The CID is an address identifying the connection between a specific source terminal and destination terminal. It is temporary and used for the single communication. After the communication between the source terminal and the destination terminal is complete, the connection is broken and the channel can be reused for another communication either between the same source and destination terminal or a new source and destination terminal. The CID can also be reused for another communication either between the same source and destination terminal or a new source and destination terminal.
In contrast, for connectionless communications, the message is sent from the source terminal to the destination terminal without first completing the set-up portion of the procedure. Sending a message in a connectionless communications networks takes much less set-up time than sending a message in a connection-oriented communications system since the set-up procedure with a NOC or network manager is not required. However, in a connectionless communications system there is no guarantee that the destination terminal will have the channel capacity available to receive the packets nor is there guarantee of resources in the on-board cell switch.
Delays could be experienced if a connection-oriented system were used to send data in a connectionless manner including a delay in establishing a connection and a delay in receiving messages. In addition, decisions must constantly be made about whether or not to maintain an idle connection, thereby tying up satellite resources, or terminating the connection and experiencing a delay in re-establishing the connection later.
With the advent of the Internet, the demand to transport data in a connectionless manner has increased tremendously. Therefore, it would be advantageous to develop a scheme to send data, such as IP data, in a connectionless manner over a system which supports connection-oriented communications and do so in a manner which is compatible with the ATM protocol used in many connection oriented systems.
U.S. Pat. Nos. 5,432,777 and 5,517,497 disclose a method for sending data in a connectionless manner over a connection-oriented network which includes assigning a routing identifier (RI) to each terminal in the network and placing a destination terminal RI in the header of each cell of the message. For this method, the source terminal consults a global lookup table which correlates each terminal in the system with an RI in a unique mapping. The source terminal places the destination terminal RI in the header of each cell. The cells are sent to a node in the system. Each node must read the destination terminal RI in the header of each cell and determine the proper routing sequence required for the cells to be transmitted to the proper destination terminal. When applied to a satellite network, this method requires resources in each satellite to read the destination terminal RI, look up the destination terminal RI in a lookup table and possibly assign a routing tag to the cell to route it through each satellite""s cell switches.
The cells are routed through each satellite to the desired destination terminal. The destination terminal only accepts cells having its individual destination terminal RI in the headers. The method disclosed in the ""777 and ""497 patents is not optimal for all communication networks. In particular, by using a unique destination terminal RI located in the header of each cell, the method disclosed in the ""777 and ""497 patents does not take advantage of the broadcast capability of a satellite network having multiple downlink antennas where each downlink antenna typically covers many destination terminals. In such a network, a single address can reach many destination terminals such that a unique destination terminal RI in the header of each cell is not required for the cell to arrive at the desired destination terminal.
After the data is routed to the proper destination terminal, the destination terminal typically must separate, or demultiplex, the cells since cells sent from different source terminals are multiplexed together before arriving at the destination terminal. To separate multiple streams of data coming from different source terminals to the same destination terminal, the ""777 and ""497 patents discloses using a multiplexing identification (MID) field in the cell headers where the value of the MID field allows, at the destination side, to identify the cells which belong to the same connectionless message. This value has to be unique. The ""777 and ""497 patents prefer that the source RI value be used as the MID and either the last ten bits of the RI value are taken as the MID or, the header is extended to allow more bits to be used. Using the MID field to demultiplex cells from different sources restricts the ATM Adaptation Layer (ML) protocol which can be used to demultiplex the cells to the ATM Adaptation Layer 3/4 (AAL3/4) protocol. A more detailed discussion of ATM Adaptation Layer protocols including the ATM Adaptation Layer 3/4 (AAL3/4) and the ATM Adaptation Layer 5 (AAL5) protocols can be found in CCITT, xe2x80x9cDraft Recommendation I.363xe2x80x9d. CCITT Study Group XVIII, Geneva, Jan. 19-29 1993. The ATM Adaptation Layer 3/4 (AAL3/4) protocol has a MID field, but, the ATM Adaptation Layer 5 (ML5) protocol does not. Therefore, the method specified in the ""777 and ""497 patents does not support the newer ATM Adaptation Layer 5 (AAL5) protocol which is typically the adaptation layer protocol of choice for IP data transfers among those skilled in the art. Thus, the scheme defined in the ""777 and ""497 patents are deficient for various network environments.
What is needed therefore is a method for sending data in a connectionless manner over a network which supports the ATM and established connections for data message transfers which takes advantage of the broadcast capabilities of a satellite system. The method should additionally support the use of higher order adaptation layer protocol, in particular, the adaptation layer 5 protocol.
The preceding and other shortcomings of the prior art are addressed and overcome by the present invention which provides, in a first aspect, a method for transferring a data packet between a first source terminal and a first destination terminal, in a communications network having a plurality of source terminals, destination terminals, satellites and downlink antenna beams where one of the downlink antenna beam covers said first destination terminal. Each data packet includes a destination address identifying a user for which the data packet is meant with the first destination terminal having the capability to reach the user.
The method includes assigning a unique downlink beam identifier to each downlink antenna beam in the communications network; mapping the destination address to a downlink beam identifier the corresponding antenna beam of which covers the first destination terminal. The data packet is segmented into one or more cells, each cell having a cell header. The downlink beam identifier is placed into each cell header and the cells are routed to the downlink antenna beam corresponding to the downlink beam identifier. The cells are broadcasted over the downlink antenna beam and received by the destination terminals located within the downlink antenna beam of which one of the destination terminals is the first destination terminal.
In a second aspect, a source terminal identifier is placed into each cell header to be used by the destination terminals to sort cells sent from different source terminals.
In a third aspect, the satellite network uses the Asynchronous Transfer Mode for data message transfers.
In a fourth aspect, the data packet in an Internet Protocol (IP) packet which includes a destination IP address.